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E4SS (ECharts for SIP Servlets) is open-source software that allows the use of the ECharts programming language to program arbitrarily complex SIP services. Instead of overriding servlet methods and managing sessions, the programmer defines the application in terms of feature boxes, SIP message ports, and state-machine logic specified in the ECharts language. The use of ECharts to specify application logic greatly encourages component re-use and manages complexity, making it well-suited for complex Back-to-Back User Agent applications.

The E4SS development kit (EDK) provides all the tools you need to develop your custom SIP Servlet application.  In addition, there is an extensive library of call-control state-machine fragments that can speed application development.  Also, the EDK includes a number of complete features with Java APIs to integrate with any environment.

Much more information, including the EDK and extensive documentation, are available at the E4SS website.
 

(c) ACM, 2010. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution.

The definitive version was published in Principles, Systems, and Applications of IP Telecommunications., 2010-08-02.

{Telecommunication services vary greatly in their behavior. However they often can be decomposed into tightly-focused components, each designed to accomplish a certain limited function. In some cases, these functions are repeated across many services that seem quite disparate at first glance. We examine some components that have proven to be highly reusable, and demonstrate how they can be composed into a variety of interesting services. }

{In this paper, we describe our experience with the design of an advanced teleconferencing service under two different frameworks -- an early implementation of the Distributed Feature Composition architecture, and the SIP Servlet API. The usual design goals of software modularity for encapsulation and reuse are pursued. Interestingly, two very different designs resulted. This paper discusses the factors that influenced our design decisions. In particular, we examine the different characteristics of the two frameworks as well as the maturity of project requirements, and illustrate the ways in which these factors affect various mechanisms for achieving software modularity. We also aim to draw on this experience to propose a set of design guidelines for building modular, composable SIP Servlet applications for Voice over IP and converged services. Final camera-ready copy for conference }

{The development of telecommunication applications that require multiple call legs is often complex due to their event-driven nature as well as the significant amount of state that must be maintained. In general, the state associated with different call legs within an application instance differs and must be separately maintained; in addition, (non-call related) application state is often required. As a means of managing all the required state information, application developers often implement ad-hoc state machine programming constructs within the application. }

{Personal mobility is probably the most desired of all telecommunication capabilities, but it presents many design difficulties. This paper explains some of the difficulties, and shows how they can be overcome with the help of a component architecture. Two component coordination mechanisms are emphasized, one novel and one used in an unusual way. These mechanisms may be useful in other distributed applications besides telecommunications. }